An earthquake is caused by a sudden release of accumulated strain energy along faults in the Earth. Energy radiates out in all directions from the focus of the earthquake. Seismographs record earthquake shaking as seismic waves that help locate the epicenter. The size of an earthquake is described by both its intensity, which measures shaking damage, and its magnitude, which estimates the amount of energy released.

1. What is an earthquake?What is an earthquake?
 An earthquake is the vibration of EarthAn earthquake is the vibration of Earth
produced by the rapid release of energyproduced by the rapid release of energy
 Energy radiates in all directions from itsEnergy radiates in all directions from its
source, thesource, the focusfocus
 Energy moves like wavesEnergy moves like waves
 Seismographs record the eventSeismographs record the event
Slinky, Rubber Band SEISMOGRAM
Beaker, Wet Sand, Weight
Cardboard Fault models
Chewing Gum
Wood meter stick or plastic ruler
pencil

2. Anatomy of EarthquakesAnatomy of Earthquakes
Earthquakes are associated with faultsEarthquakes are associated with faults

3. ) ) ) ) ) ))((( ( ( ( (
Earthquakes are causedEarthquakes are caused
by sudden release ofby sudden release of
accumulated strain energyaccumulated strain energy
along Faultsalong Faults
Rocks onRocks on
sides of faultsides of fault
are deformedare deformed
by tectonicby tectonic
forcesforces
Rocks bendRocks bend
and storeand store
elastic energyelastic energy
FrictionalFrictional
resistanceresistance
holding theholding the
rocks togetherrocks together
is overcomeis overcome
by tectonicby tectonic
Hands Demo

4.  Earthquake mechanismEarthquake mechanism
– Slip starts at the weakest point (the focus)Slip starts at the weakest point (the focus)
– Earthquakes occur as the deformed rockEarthquakes occur as the deformed rock
“springs back” to its original shape (“springs back” to its original shape (elasticelastic
reboundrebound))
– The motion moves neighboring rocksThe motion moves neighboring rocks
– And so on.And so on.
– DEMO – elastic rebound w/ rulerDEMO – elastic rebound w/ ruler

5. RelationshiRelationshi
p Betweenp Between
Stress andStress and
StrainStrain
Strain can be a change in shape (a deformation) due to an applied stress
Demo: Rubber Band

6. RelationshipRelationship
BetweenBetween
Stress andStress and
Strain at lowStrain at low
Temps andTemps and
Pressure orPressure or
Sudden StressSudden Stress
Demo: Pencil

7. RelationshipRelationship
BetweenBetween
Stress andStress and
Strain underStrain under
High TempsHigh Temps
or Pressureor Pressure
Demo: gum

8. Strike and DipStrike and Dip
Strike intersection w horizontal, dip perpendicular, angle from horizontal down toward surface
Strike is long line, dip is short line
Note the angle of dip given 45o

9. VerticalVertical
MovementMovement
along Dip-Slipalong Dip-Slip
FaultsFaults
Divergent
Convergent

10. Horizontal Movement AlongHorizontal Movement Along
Strike-Slip FaultStrike-Slip Fault

11. Normal Fault Quake - NevadaReverse Fault Quake - Japan
Strike Slip Fault Quake - California
DEMO – Types of faults

12. Fence offset by the 1906Fence offset by the 1906
San Francisco earthquakeSan Francisco earthquake
 San Andreas is the most studied transform faultSan Andreas is the most studied transform fault
system in the worldsystem in the world
 discrete segments 100 to 200 kilometers longdiscrete segments 100 to 200 kilometers long
 slip every 100-200 years producingslip every 100-200 years producing
large earthquakeslarge earthquakes
 Some portions exhibit slow, gradual displacementSome portions exhibit slow, gradual displacement
known as fault creepknown as fault creep

14. Fires caused by 1906 San Francisco Earthquake
Gas mains break, fires shaken out of furnaces. Water mains break, cannot
fight fires. Debris in streets, Fire department cannot reach fires.

15. Landscape Shifting, Wallace CreekLandscape Shifting, Wallace Creek
San Andreas Fault, a Transform Margin

16. LiquefactionLiquefaction
Demo: Liquifaction

17. SeismographSeismograph
 Data-data aktual getaran tanah dariData-data aktual getaran tanah dari
seismograph dikenal sebagai sebuahseismograph dikenal sebagai sebuah
seismogram, dapat menyediakanseismogram, dapat menyediakan
informasi tentang gempa secara alami.informasi tentang gempa secara alami.
 Data-data seismograph terdiri dari:Data-data seismograph terdiri dari:
 Percepatan terhadap waktuPercepatan terhadap waktu
 Kecepatan terhadap waktuKecepatan terhadap waktu
 Perpindahan terhadap waktuPerpindahan terhadap waktu

18. SeismographSeismograph
 Sebuah seismograph adalah sebuah instrumen yangSebuah seismograph adalah sebuah instrumen yang
mencatat, sebagai fungsi waktu, geteran permukaanmencatat, sebagai fungsi waktu, geteran permukaan
bumi akibat timbulnya gelombang-gelombang seismicbumi akibat timbulnya gelombang-gelombang seismic
oleh gempabumi.oleh gempabumi.
 Data-data aktual getaran tanah dari seismograph dikenalData-data aktual getaran tanah dari seismograph dikenal
sebagai sebuah seismogram, dapat menyediakansebagai sebuah seismogram, dapat menyediakan
informasi tentang gempa secara alami.informasi tentang gempa secara alami.

19. SeismographSeismograph
 Data-data seismograph terdiri dari:Data-data seismograph terdiri dari:
 Percepatan terhadap waktuPercepatan terhadap waktu
 Kecepatan terhadap waktuKecepatan terhadap waktu
 Perpindahan terhadap waktuPerpindahan terhadap waktu

20. SeismologySeismology
SeismometersSeismometers - instruments that- instruments that
record seismic wavesrecord seismic waves
Records the movement ofRecords the movement of
Earth in relation to a stationaryEarth in relation to a stationary
mass on a rotating drum ormass on a rotating drum or
magnetic tapemagnetic tape

21. A seismograph designed toA seismograph designed to
record vertical ground motionrecord vertical ground motion
The heavy mass doesn’t move much
The drum moves

22. Lateral Movement DetectorLateral Movement Detector
In reality, copper wire coils move around magnets, generating current which is recorded.

23. Seismic Waves 1: Surface wavesSeismic Waves 1: Surface waves
–Complex motion, great destructionComplex motion, great destruction
–High amplitudeHigh amplitude and low velocityand low velocity
–Longest periods (interval between crests)Longest periods (interval between crests)
–Termed long, or L wavesTermed long, or L waves

24.  Types of seismic waves (continued)Types of seismic waves (continued)
 Body wavesBody waves
– Travel through Earth’s interiorTravel through Earth’s interior
– Two types based on mode of travelTwo types based on mode of travel
– Primary (P) wavesPrimary (P) waves
 Push-pull motionPush-pull motion
 Travel thru solids, liquids & gasesTravel thru solids, liquids & gases
– Secondary (S) wavesSecondary (S) waves
 Moves at right angles to theirMoves at right angles to their
direction of traveldirection of travel
 Travels only through solidsTravels only through solids

25. Smaller amplitude than surface (L) waves, but faster, P arrives first, then S, then L
P and S waves
Demo: P and S waves

26. Earthquake focus andEarthquake focus and
epicenterepicenter

27. Note how much bigger the surface waves are

28. Graph to find distance toGraph to find distance to
epicenterepicenter

29. Locating Earthquake EpicenterLocating Earthquake Epicenter

30. Epicenter located using threeEpicenter located using three
seismographsseismographs

31. 95% of energy released by earthquakes originates95% of energy released by earthquakes originates
in narrow zones that wind around the Earthin narrow zones that wind around the Earth
These zones mark of edges of tectonic platesThese zones mark of edges of tectonic plates
Broad are subduction zone earthquakes, narrow are MOR. Lead to recognition of plates

32. Earthquake Depth and Plate TectonicEarthquake Depth and Plate Tectonic
SettingSetting
Subduction Zones discovered by Benioff

33. Earthquake in subductionEarthquake in subduction
zoneszones

34. Earthquakes at DivergentEarthquakes at Divergent
Boundaries - IcelandBoundaries - Iceland
Crust pulling apart – normal faults

35. Measuring the size ofMeasuring the size of
earthquakesearthquakes
 Two measurements describe the size of anTwo measurements describe the size of an
earthquakeearthquake
IntensityIntensity – a measure of earthquake shaking– a measure of earthquake shaking
at a given location based on amount ofat a given location based on amount of
damagedamage
MagnitudeMagnitude – estimates the amount of energy– estimates the amount of energy
released by the earthquakereleased by the earthquake

36. Intensity scalesIntensity scales
Modified Mercalli Intensity ScaleModified Mercalli Intensity Scale waswas
developed using California buildings as itsdeveloped using California buildings as its
standardstandard
Drawback is that destruction may not beDrawback is that destruction may not be
true measure of earthquakes actual severitytrue measure of earthquakes actual severity

37. Magnitude scalesMagnitude scales
Richter magnitudeRichter magnitude - concept introduced by- concept introduced by
Charles Richter in 1935Charles Richter in 1935
Richter scaleRichter scale
–Based on amplitude of largest seismicBased on amplitude of largest seismic
wave recordedwave recorded
–LOGLOG1010 SCALESCALE
Each unit of Richter magnitudeEach unit of Richter magnitude
corresponds to 10X increase in wavecorresponds to 10X increase in wave
amplitude and 32X increase in Energyamplitude and 32X increase in Energy

38. Magnitude scalesMagnitude scales
Moment magnitudeMoment magnitude was developed becausewas developed because
Richter magnitude does not closely estimateRichter magnitude does not closely estimate
the size of very large earthquakesthe size of very large earthquakes
–Derived from the amount of displacementDerived from the amount of displacement
that occurs along a fault and the area ofthat occurs along a fault and the area of
the fault that slipsthe fault that slips

39. TsunamisTsunamis, or seismic sea waves, or seismic sea waves
Destructive waves called “tidal waves”Destructive waves called “tidal waves”
Result from “push” of underwater faultResult from “push” of underwater fault
or undersea landslideor undersea landslide
In open ocean height is > 1 meterIn open ocean height is > 1 meter
In shallow coast water wave can be > 30In shallow coast water wave can be > 30
metersmeters
Very destructiveVery destructive

40. Formation of a tsunamiFormation of a tsunami
Tsunamis are actually huge, extending from
the fault on the sea floor up to the surface, but
they don’t stick up more than a meter or so in
the deep ocean. However, when they reach
shallow water they must rear up and slow
down. Discussion: Kinetic vs. potential energy

41. Honolulu officials know exactly how
long it takes a Tsunami to reach
them from anywhere

42. Tsunami 1960,Tsunami 1960,
Hilo HawaiiHilo Hawaii

43. TsunamiTsunami
Model,Model,
AlaskaAlaska
QuakeQuake

44. Earthquake predictionEarthquake prediction
 Long-range forecastsLong-range forecasts
Calculates probability of a certainCalculates probability of a certain
magnitude earthquake occurring over amagnitude earthquake occurring over a
given time periodgiven time period
 Short-range predictionsShort-range predictions
Ongoing research, presently not muchOngoing research, presently not much
successsuccess

45. Long Term Predictions
Seismic Gaps

46. Seismic Gaps at the Aleutian Islands SUBDUCTION ZONE

47. Seismic Gap along HimalayasSeismic Gap along Himalayas
2005

48. 4848
Dilatancy of Highly Stressed RocksDilatancy of Highly Stressed Rocks
Short-Term Earthquake Prediction

49. Investigating Earth’s InteriorInvestigating Earth’s Interior
 Seismology helps us understand Earth’sSeismology helps us understand Earth’s
Interior Structure. We use:Interior Structure. We use:
 Speed changes in different materialsSpeed changes in different materials
due changes rigidity, density, elasticitydue changes rigidity, density, elasticity
 Reflections from layers with different propertiesReflections from layers with different properties
 Attenuation of Shear Waves in fluidsAttenuation of Shear Waves in fluids
 Direction changes (Refraction)Direction changes (Refraction)

50. 5050
Investigating Earth’s InteriorInvestigating Earth’s Interior

51. Surface Components magnifiedSurface Components magnified
!

52. Seismic-wave velocities are faster in the upper mantleSeismic-wave velocities are faster in the upper mantle
Waves that travel via mantle arrive sooner at far destinations
Velocity increases w depth, waves bend back to surface.
Mohorovičić discontinuity

53. Wave VelocitiesWave Velocities
Upper Mantle Fast
Asthenosphere
Slow
Lower Mantle Fast

54. The S-Wave Shadow ZoneThe S-Wave Shadow Zone
Since Shear (S)
waves cannot travel
through liquids, the
liquid outer core
casts a larger shadow
for S waves covering
everything past 103
degrees away from
the source.
http://en.wikipedia.org/wiki/Richard_Dixon_Oldham

55. The P-Wave Shadow ZoneThe P-Wave Shadow Zone
Behavior of waves through center reveal Earth’s Interior
P-waves through the liquid
outer core bend, leaving a
low intensity shadow zone
103 to 143 degrees away
from the source, here
shown as the north pole
HOWEVER, P-waves
traveling straight through
the center continue, and
because speeds in the
solid inner core are faster,
they arrive sooner than
expected if the core was
all liquid.
Inge Lehmann
http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_lehmann.html